This invention relates to the automatic calibration of electronic instruments and more particularly to the automatic calibration of a pH measuring system.
In presently available pH meters it is necessary to manually calibrate the instruments for voltage offsets in the electrodes and in the electronics. This is a time consuming job and the accuracy depends upon the operator. The usual manual calibration method includes balancing a high impedance difference amplifier. The operator observes a meter and adjusts the balance until the meter nulls. If more than one calibration point is used, error often results. In making a calibration, it is necessary to set both the slope and the zero offset.
Our copending application Ser. No. 453,794 filed Mar. 22, 1974 is directed to setting the slope of the instrument.